Robust qubit memory is essential for quantum computing, both for near-term devices operating without error correction, and for the long-term goal of a fault-tolerant processor. We directly measure the memory error ϵm for a 43Ca+ trapped-ion qubit in the small-error regime and find ϵm<10−4 for storage times t≲50\mboxms. This exceeds gate or measurement times by three orders of magnitude. Using randomized benchmarking, at t=1\mboxms we measure ϵm=1.2(7)×10−6, around ten times smaller than that extrapolated from the T2∗ time, and limited by instability of the atomic clock reference used to benchmark the qubit.
@article{arxiv.1905.06878,
title = {Probing Qubit Memory Errors at the Part-per-Million Level},
author = {M. A. Sepiol and A. C. Hughes and J. E. Tarlton and D. P. Nadlinger and T. G. Ballance and C. J. Ballance and T. P. Harty and A. M. Steane and J. F. Goodwin and D. M. Lucas},
journal= {arXiv preprint arXiv:1905.06878},
year = {2019}
}